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H. L. BAR/VE Y .6. PETERSON R. K. POTTER By mmsenks ,4T ORNE /N VEN TORS Patented Nov. 28, 195@ ELECTRON BEAM TUBE FILTER Harold L. Barney, Madison, Liss C. Peterson,

Chatham, Ralph K. Potter, Madison, and Raymond W. Sears, West Orange, N. J., assignors to Bell Telephone Laboratories, Incorporated New York, N. Y., a corporation of New York Application February 4, 1949, Serial No. 74,616

' la Claims. l

This invention relates to the modification of time-varying functions in accordance with preselected patterns; more particularly, it relates to electrical transducers of the type which are sidered from the time function point of view, that is when time rather than frequency is taken as the independent variable, one is led to a broad group of selective circuits whose principle of operation does not depend upon resonant combinations of network elements.

A certain class of devices which are knownin the art as transversal filters, substitute the time function approach for the conventional steadystate approach in the simulation of network response, operatingv through a series of steps which include the follow-ing:

tions of time in accordance with desired patterm of amplitude, frequency, and phase variation.

A more specific object of this invention is tt provide inta transversal filter an improved sysknown in the art as transversal filters. 5 tem for collecting and weighting samples of thu The behavior of electrical networks can be stored record. specified in two ways representing two different The present invention relates broadly to i physical points of view. Ordinarily, one thinks f transversal iilter in whichthe input signal i: first of the well-known steady-state point of view stored as a series of parallel records in spacl which describes the network performance in l0 which vary from one to another in accordancl terms of the concepts of amplitude and phase rewith the values of a given input function durim sponse versus frequency. In addition to this cach of a succession of equal time intervals, anc more conventional viewpoint there is the time in which the samples to be weighted are derive( function one in which the network is described during corresponding time intervals by neutralin terms of its magnitude time response at the izlng points on each of the stored records in roreceiving end resulting. from the amplitude of an tation in such a manner that the neutralize: impulse of infinitesimal duration at the sending points liealong a succession of parallel line: end. Network response may thus be considered which intersect the records obliquely. The deeither in terms of frequency or time functions. rived samples are weighted in rotation in accord- The bridge between these two avenues of apance with selected values of a chosen weighting proach is the Fourier integral which may be function, and successively integrated to form thl thought of as a mathematical device for expressdesired output function. ing a time function in terms of steady-state phe- In certain systems disclosed by L. C. Petersor nomena. and R. K. Potter in application Serial No. 731,232 For the most part prior art practice has been filed February 27, 1947, the function of storing z to base the design of communication networks record 0f the input Signal. Weighting samples 0 upon the steady-state frequency amplitude charthe stored record, and integrating the weightec acteristics and an elaborate theory has been samples in a preselected order is performed in s Worked out for such design procedures.' The net cathode-ray tllb- The afOreSad tube has 2 Ye works thus obtained contain as elements resistcording beam intensity varied in accordance wit] ances, inductances and capacitances, the frethe impressed Signal WhCh SCaIlS and deDOSit quency and/ory phase selective eiects of which charge on a target comprising a plurality of ele are used in various combinations to secure desired ments which are either shaped 0r Potential Varie' response characteristics. in accordancewith a selected weighting function On the other hand when network design is conand a wiping beam moving in synchronism wit] the recording beam to collect the weightel charges from the target through secondary emis sion paths and integrate them in a common out put circuit. In accordance with another modi cation disclosed by Peterson and Potter supra the weighted elements of charge are collecte from the target elements by means of a rotatin switch' moving synchronously with the recordin beam.

AA preferred embodiment of the transverse lter of the present invention comprises a cath oderay tube which utilizes a single beam fc both recording and wiping operations, the bear being switched in succession from a vertical re cording position to oblique wiping positions pre ceding and following the recording beam.y Th target over which the beam moves comprises rectangular insulating sheet, such as mica, on th back of which is disposed a plurality of space metallic strips in transverse parallel relatior Attached to each of the metallic backing strip is a circuit including' a weighting resistor value in accordance with a -selected ordinate of the chosen weighting function, ali of the weighting resistors being connected together through a series of gating circuits to a common output Junction. The input signal is introduced into the system by means of a barrier grid interposed in front of the mica target sheet and having a few thousandths of an inch separation therefrom. The complex scanning motion of the beam, which executes a series of vertical recording lines in alternation with oblique scanning lines, is controlled by two pairs of electrostatic deflection plates to which is connected a multielement sweep circuit. In synchronism with the switching of the beam the potential of the barrier grid ls shifted so that during the vertical recording position the potential of the grid is varied in accordance with the input signal, while during the wiping operation the potential of the grid is changed to a constant value to enable the .charge recorded on the target to be neutralized. Currents proportional to the recorded charge are thus enabled to flow from the respective target backing strips during the wiping operation and through the weighting circuits to the common output circuit where they are integrated in successive groups to produce a modified output current.

Additional objects and features of the invention will be apparent after a study of the detailed description which follows hereinafter, and the attached drawings, of which:

Figs. 1A to 1E are diagrams illustrating the theory of operation of transversal filters;

Figs. 2A and 2B show graphical interpretations of two specific filter characteristics;

Fig. 3A is a preferred embodiment of a complete system in accordance with the present invention utilizing a cathode-ray tube having an electron beam focussed in the plane of the target electrode which executes a series of vertical recording scans preceded and/or followed by oblique wiping scans;

Fig. 3B is a plan view of the multielement target 3i!) of Fig. 3A;

'Fig'. 3C is a, detailed cross-sectional view of the multielement target 3m and the barrier grid 302 of Fig. 3A;

Figs. 1C-4G are details of construction of alternate forms ofthe barrier grid 3|2 of Fig. 3A;

Fig. 5A shows diagrammatically the scanning motion executed by the beam of Fig. 3A;

Figs. 5B and 5C respectively, represent the X land Y sweep voltages impressed on the deflection plates 3| I and 309 of Fig. 3A;

Fig.' 6 shows in schematic a preferred embodiment of the X-axis sweep circuit included in the system fo Fig. 3A;

Figs. 'lA-F indicate voltage points in the circuit of Fig. 6;

Fig. 8 shows schematically an alternative form of the X-axis sweep circuit which could be substituted for the circuit shown in Fig. 6.

Figs. 9AD indicate voltage forms at various points in the circuit of Fig. 8;

' Fig. l0 is a graph illustrating the use of a typical weighting function in the system of Fig. 3A; and

forms at various Figs. 11A-C illustrate graphically the manner in which the beam functions to deposit and collect charge on the target 3I in the system of .A concept which may be helpful in interpreting the specification and claims hereinafter is that of the transfer indicia] admittance of a sysa upon the history tem. This quantity is dened by J. R. Carson in Electric Circuit Theory and the Operational Calculus, McGraw-Hill, 1926, page 14, as the ratio of the output current of the system, expressed as time function, to the magnituie'of the steady electromotive force suddenly inserted at the input of the system at time t=0.

The time rate-of-change of the transfer indi- 1 cial admittance defined above is a function of time designated g t). The function g(t) is variously referred to in the specification and claims hereinafter as the impulse response or merely the g-function of a system.

Further discussion and definition of certain mathematical concepts, such as that of the lunit impulse, which will be relied on in the detailed description hereinafter will be found in Volume I of Transients in Linear Systems by Gardner and Barnes, John Wiley and Sons, 1942, pages Z55-263.

The broad function point Figs. 1A to 1E, Consider a frequency selective network such as is illustrative schematically by N in Fig. 1A. Let us assume that the complex voltage wave Eft) shown in Fig. 1B which is any continuous function of voltage versus time, is impressed upon i of the network. At the output 2 there will then appear a. current wave which We designate as lit). Now let it be supposed that the voltage wave EG) is split up into a series of narrow pulses as shown in Fig. 1C. With this pulsed wave impressed upon the input terminals I, one should expect to obtain at the output terminals 2 very nearly the same current wave I(t) obtained before.

Now referring to Fig. 1D, assume that there is impressed upon the network a single pulse of the sort into which the voltage wave Ed) has been subdivided. At the network output terminals 2 there now appears a function which as the pulse width approaches zero is proportional to the y-function o f the network as defined above. It should be noted that any other pulse or different amplitude would result ln the approximate g-function except that its amplitude would vary in proportion to the applied puise ampliprinciples upon which the timeof view is based are illustrated in would depend on the time of pulse application. Thus it follows as shown limit the current wave I(t) which appears at the output terminals 2 as a result of the application of the voltage wavey E( t) at the input terminals I is the sum of a number of overlapping g-functions whose relative strengths or amplitudes vary in accordance with the impressed voltage wave E(t). cise language one can say that if the network is subjected at the input I to an initial pulse at some arbitrary time, which for convenience may be called zero, and if this pulse is followed-by others at specified values of time, the total response at the output terminals 2 at any later time will be the sum of the responses which have occurred up to that time.

Thus, two important principles applicable to this approach to network theory may be derived from the above. First, the network response to unit impulse of infinitesimal duration completely determines the response to any other input wave. Second, the response at any time depends of the applied input wave previous to the time in question so that the past history must be available at least over a time into which reference is now made.

in Fig. 1E that in the Using somewhat more preterval within which the g-function is of appreclable magnitude.

Therefore the network can be locked upon as a circuit for effecting the summation of a series of time displaced g-functions in which the individual amplitude of each of the respective gfunctions is proportional to the corresponding time displaced instantaneous value of the impressed voltage wave E(t) This process is schematically indicated in Fig. 1E.

Adopting a slightly different point of view one can also look upon the output wave as representing at any time a weighted history or record of the input wave where the g-function has acted as the weighting factor.

The foregoing statements may be summarized by deriving a mathematical expression for the network response to an arbitrary driving force from the assumption that the net behavior of a linear system at any instant is a function of the linear superposition of all the responses which have occurred up to that time counting from some arbitrary starting point. Assume, for example, that a network is subjected to an initial voltage pulse E(t) at the time t= and that this pulse is followed by others at specified values of time. Then the total response at any later time will be the sum of the responses which have occurred up to that time, due allowance being made for the time at which each pulse was applied.

Let the time axis then be divided into short intervals A-r of equal width, the electromotive force EM) being approximated by a series of rectangular pulses applied for the duration of each time interval A-r. time t is then approximately the sum at that instant of all the elementary responses started previous to that instant. If the interval A-r is very small, that is, approaches zero as a limit, the response at time t to the first impulse is i1-Ew) g(t) where g(t) is the response to unit impulse or gfunction as dened hereinbefore, where E(0) is the amplitude of the voltage wave E(t) at time t=0. Consider now the (n+1)th impulse. The response at time t is EULA?) A-rg(t-nA-r) In this expression it should be noted that nAiis the time of impulse application. The reason that the argument of the g-function in this latter expression is t-nA-r and not t is that this pulse does not come into existence until the time nA-r and the expression is only valid for the time equal to or greater than nA-r. Assume an arbitrary point on the time scale to be denoted by r, thus r=nAr. The current response I(t) at the instant t is the sum at time t of all elementary responses that have occurred between time equal to 0 when the first impulse was started and time t as the length of the time interval Av approaches zero. Hence By definition of an integral this may also be written T= Ic) :i120 En EoiAfgo-f) MFLt Ecm-ndr (2i The total response at a specified v knowledge of the response g('t) to a unit impulse is suflicient to specify completely the system performance. This implies in particular that the steady-state performance of a particular network may also be determined from a knowledge of g(t) for that network. Suppose, for example, that the network is a filter passing a certain band of frequencies. This is then merely a. reection of the fact that g(t) behaves in a very definite manner. To illustrate this in a general way, assume that a sinusoidal voltage E(t)=E sin wt, where E represents the steady-state amplitude and w=the angular frequency, has been applied to the network at t=0; and that all transients have died out. The steady-state current can then be writtenas where Y12(w) is the transfer admittance between input and output terminals of the selected network and om) its phase angle. By writing Yrzw) =ai2(w) +ib1z(w) in which aiz and bis are constants, the second of expressions (3) is obtained. An equivalent expression may also be obtained from (2) or (2') by inserting E(t)=E sin wt and extending the range of integration to innity (which means that transient distortion had died out) one obtains,

Io) =E sin mi @es ligam- E COS art: sin wig('r)d1' By comparison of (3) and (4) it follows that (5) b12(w)=-L sin wigmdf The points to be emphasized ingeneral are, first, that the expressions (5) establish quantitative relations between the frequency selection properties of the networks and the response to unit impulse excitation; and second, that both the real and imaginary components of the transfer admittance can be calculated from a knowledge of the response vto unit impulse. This relationship may also be further illustrated as follows: Multiply the second of Equations 5 with z', the imaginary unit, and add to the first; then use Eulers formula. The result is Y1, (is) :Lm gaie-mdf (e) from 'which it follows that the steady-state transfer admittance is the Fourier transform of the unit impulse response. From a principal point of view, it is thus irrelevant whether frequency selection properties of a network are stated in terms of steady-state frequency response to sinusoidal driving forces or whether they are given as the time response to a unit impulse. The frequency response is merely the spectral analysis of the time response to a unit impulse. It also follows from-(6) that where Y1a(iw) denotes the amplitude and @(w) the phase of the steady-state transfer admittance. Equation 7 in principle allows g(t) to be calculated from a knowledge of the frequency spectrum of the steady-state transfer admittance. i. e. from the amplitude frequency and phase characteristics of the network. Moreover, we have from 1. Recording or storage of the input wave;

2. Deriving samples of the stored record, weighting of the said samples by means of g-waves; and

3. Summing the weighted samples of the record.

These are fundamental steps which can serve as building blocks in frequency selective devices operating on a time function basis. It should be noted that in arriving at these steps no reference has been made to vibrating systems such as coil and condenser combinations nor has any use been made of the concepts of amplitude and phase versus frequency response. 'I'hese concepts have now been replaced by the single concept of the g-wave. In other words the physical phenomena conventionally described by the amplitude and phase versus frequency functions are now described by the single function g(t).

As concrete examples of g-functions, consider two cases of functions in which the positive and negative values aresymmetrical with respect to a certain value of time, say time To, where To 0. Consider first a low-pass filter having a uniform transfer impedance equal to K from frequency zero to a cut-off angular frequency we. Outside this range it is assumed that no transmission occurs. As a consequence of the stipulation of .even time response, the phase shift @(w) is linear and is given by the following equation:

For the low-pass filter under consideration we thus obtain by substituting the above in Equation 7 This function is shown as Fig. 2A. It may be demonstrated that the width of the main oscillatory lobe is inversely proportional to the band width fc. It is also seen that the received signal reaches its maximum at the time t-To and that the maximum response is proportional to the area MK under the amplitude characteristic.

As a second example we consider an idealized band pass lter of even time response and with a flat amplitude characteristic between the cutoff frequencies wei and :vez (wc-2mm). Outside this frequency range it is assumed that no transmission can take place. From (7) and (11) which may be reduced to Here w represents the band width ocr-wei and wm the arithmetic mean of the two cut-off frequencies wci and wcz and may thus be considered to coincide with the mid-band frequency. Equation 11 which is roughly plotted on Fig. 2B represents an amplitude modulated carrier wave with a carrier frequency equal to that of midband. The maximum response occurs at t-To and is proportional to wK which is the area under the amplitude response characteristic and the length of the main oscillatory lobe is which is inversely proportional to the band width.

The operations which are described theoretically in the foregoing pages of the specification, namely, the recording and storing of the impressed input signal, taking samples of the stored record in a predetermined sequence, and weighting and collecting the samples in a. common output, are performed in accordance with one embodiment of the invention by a circuit such as shown in Fig. 3A of the drawings including a cathode-ray tube in which the recording and sampling operations are controlled by a single focussed beam alternately switched to different positions. 'I'he beam moves over a mica target. on the back of which are positioned a plurality of transverse parallel metal bars, each of which is connected to a common output through a resstance of a preselected value. Horizontal and vertical deection plates located in the tube control the motion of the beam progressively over the target in a configuration such as indicated in Fig. 5A of the drawings. During the recording operation, in which the beam traces a vertical line on the target, the potential of a barrier grid adjacent the target is signal varied producing a record of charge on the target; during the wiping operations in which the beam moves across the target in a direction obliquely related to and immediately preceding and following the vertical recording line, the potential of the barrier grid is maintained at a constant value to enable the recorded charge to be neutralized. During neutralization,l increments of current flow from the transverse bars on the back of the target, through the connected weighting resistances, and into the common output circuit to produce an output currentv modified in accordance with the desired characteristic.

Referring to Fig. 3A in detail; the cathode-ray tube 30| contains a target mosaic 3I0 disposed near the large end thereof with its surface substantially normal to the electron beam 302. The source of this electron beam 302 is an electron gun assembly comprising cathode 303, intensity grid 304a, focussing anode 3041:, and anode 306 which are constructed in a manner Well known in the art to produce a pencil beam having a cross-sectional diameter at the point of focus of the order of mils. For the purpose of the system described herein, it is desirable to have the beam intensity as high as is possible without producing a defocussing of the beam. In an embodiment of the system constructed, for example, the beam currents were of the order of 50 microamperes. Normal direct-current operating biases for these elements of the electron gun are respectively supplied by potential sources 305 and 301. By means of a complex system of sweep circuits which will be described in detail hereinafter, deflection plates 300 and 3H control the electron beam so that its point of impact on the mosaic 3I0 moves along a path as previously described. An additional electrode Ia for adjusting the electrostatic field in the neighborhood of the target 3I0 comprises a conductive coating of a material such as, for example, graphite, which is applied with a uniform thickness of a few mils to the inner surface of the bulb 30|, extending from the place where the bulb flares to a position nearly adjacent the target 3I0. The aforesaid conductive coating constituting electrode 30Ia may be operated at ground potential, contact to ground being made through a conductor extending through an airtight seal in the bulb 30|. Alternatively, optimum operation may be found with this electrode connected to a direct-current potential source to provide either positive or negative bias with respect to ground.

The target mosaic 3I0 comprises a thin sheet of insulator 3I3 such as mica, with a fine mesh grid 3I2 held a few thousandths of an inch in front of the mica surface. The barrier grid 3I0 is essentially a fine mesh screen stretched parallel to the flat face of the dielectric surface 3I3 and spaced a few thousandths of an inch in front of it. The arrangement is indicated in Fig. 3C of the drawings, which is a detailed cross-sectional showing of the mosaic 3I0 in which 3I0 is a metal ring tightly fitted around the periphery of the dielectric element 3I3 to hold the barrier grid 3I2 in place; 3I3 is a mica spacing washer inserted between grid 3I2 and the dielectric surface 3I3 and 3I4' is a retaining ring inserted on the other side of the dielectric surface 3I3 to hold it in place. The mesh should be of sufiicient fineness that the electron beam cross-section covers a number of openings thereof.

Several types of mesh have been found suitable:

(l) Conventional woven wire mesh (nickel) with about 200 to 400 wires to the inch, such as indicated in Figs. 4A and 4B; or

(2) Mesh made electrolytically using photoengraving techniques, such as indicated in Figs. 4C to 4D.

It is necessary to have the grid tightly stretched across a ring for the assembly shown in Fig. 3A. One method of doing this is indicated in Figs. 4E, 4F and 4G. The mesh is first stretched across hoops I and I in much the same manner as cloth is stretched in embroidery hoops, as indicated in Fig. 4E. An edge of the mounting ring R is coated with a thin layer of brazing solder, as indicated in Fig. 4F. Then assemblies of Figs. 4E and 4F are laid together on a lavite block as indicated in Fig. 4G, and heat treated in a hydrogen furnace at a temperature just sufllcient to braze the mesh and ring R together. After removal from the hydrogen oven the excess mesh on the outside of R is cut off and the mesh remains tightly stretched across R.

In order to obtain the grid tightly stretched across the ring R it is preferable to have the expansion coefficients of the various materials related as follows:

Expansion coemcients of I and I' should be larger than mesh 2 so that as assembly c is heated to the brazing temperature, rings I and I' expand more than mesh 2 and the mesh is thereby stretched.

Expansion coefficients of ring R should be less than mesh 2 so that when unit c reaches the brazing temperature, the ring R is brazed to the mesh, and as the oven cools the mesh contracts more than ring R thus stretching the mesh very tightly across the ring R.

A typical set of materials and their expansion coefcients is as follows:

Hoops I-Monel (a copper-nickel alloy), exp.

coei`.=15 10'6 Mesh Z-Nickel, exp. coef.=13.5 106 Ring R-An alloy known as Kovar comprising 29 percent nickel, 17 per cent cobalt, 0.3 per cent manganese, and the remainder iron, exp. coef.=6 106 four such bars are shown in Figs. 3A and 3B to simplify the description of the system, a practical lter would generally require many more. Of the order of 50 to 100 of these bars might be required to simulate an actual g-function. For

example, in one embodiment constructed, the

target comprised a mica sheet about 1.25 inches square, and 0.0011 inch thick, having 13 horizontal pick-up bars on the rear face thereof, each 0.079 inch wide, and spaced apart by 0.01 inch. 'Ihe `bars or strips were deposited on the face of the mica sheet by evaporating gold in vacuum prior to assembly of the target in the final tube.

The path of the electron beam spot over the target mosaic 3I0 describes a series of alternatively vertical and diagonal lines, as indicated diagrammatically in Fig. 5A wherein the vertical lines represent the motion of the beam during the signal recording operation, and the oblique lines represent motion of the beam during the wiping or neutralizing operation which precedes and follows recording. The X and Y sweep potentials which are applied to deection plates 3| I and 309 to secure this sweep pattern are respectively indicated in Figs. 5B and'5C, and result from operation of a combination of circuits the operation and structure of which will now be described in detail.

The Y-axs sweep voltage has a simple sawtooth wave shape. The X-axis voltage remains constant during one half cycle so that the spot moves up the mosaic 3I0 along a vertical line. During the other half cycle, the spot moves down the mosaic at a constant rate, but the X-axis voltage causes it to follow a diagonal to the righthand edge of the mosaic 3I0, thence directly across to the left-hand edge in a minimum length of time, then on down a diagonal to the bottom edge of the mosaic to a point slightly to the right of the preceding vertical spot trace. From this point it again moves vertically, following the same sequence as just described. After this sequence has been repeated to the point where the vertical line is at the right-hand edge of the mosaic 3 I0, the pattern starts over at the left-hand edge. This transition is accomplished by giving the X-axis sweep voltage the wave shape shown in the middle of Fig. 5B, where the horizontal sections of the wave have progressed to the top, and the cycle is again repeated, starting at the bottom of the pattern.

The cyclic repetition rates of the Wave forms indicated in Figs. 5A and 5B are determined by certain constants which in the discussion hereinafter will be designated as follows:

Zfo-frame frequency; afascanning frequency, or lines per second; and a/Z-number of lines per frame.

In one embodiment constructed by the applicant, a was given a value of 98, and ,fo a value of 102.04 cycles per second, making the scanning frequency equal to 10,000 lines per second. The controlling frequency for both the X and Y sweep circuits is generated in a conventional sine wave oscillator 326, which is operated at the frequency afo.

'I'he output of the oscillator 326 divides, part being applied to phase shifter 321, and part to a frequency step-down unit 342. The phase shifter 321 is of the continuously variable electrostatic type such as shown on Fig. 56d, page 942 of F. E. Termans Radio Engineers Handbook, lrst edition. The output of phase shifter 321 is dlvided, part being impressed on the square wave generator 33|, and the other part on amplifier 365. Square wave generator 33| which has asquare wave output of frequency ajo, as indicated in Fig. 7E, may comprise a,circuit such as shown on Fig. 76, page 970, of F. E. Termans Radio Engineers Handbook, first edition, which is designed to produce a symmetrical square Wave when a sine wave of sufficient amplitude is applied to its input. The output of the square Wave generator 33| is separated into three parts, one of which is impressed on the X-'axis sweep voltage generator 339, and the second part of which is impressed on the amplifier 353, whose output drives the input gating circuit utilizing crystal diodes 358, in a manner which will be described hereinafter. A third part of the output of square wave generator 33| is passed through an integrating network comprising large condenser 336 and large resistance 336 to ampliiier 335. With a square wave input to the integrating circuit comprising condenser 338 and resistance 336, the output wave shape is triangular, as shown on' Fig. 5C. After amplification in amplifier 335, the aforesaid triangular wave is applied to vertical deflection plates 309.

Considering, now, particularly that portion of the output of oscillator 326 which is impressed on the frequency step-down unit 342, the oscillator frequency afo is stepped down by a ratio of a to a frequency fo. Preferably, the frequency' step-down circuit 342 is of the multivibrator type employing three pairs of push-pull stages, such as described on pages 512, 513 and 514 of F. E. Termans Radio Engineers Handbook, rst edition. The output of frequency step-down circuit 342 divides with one part being impressed on the square wave generator 350, which is substantially similar to square wave generator 33| previously described. The output of square wave generator 350 which has a frequency of fo, is impressed on the X-axis sweep voltage generator 339.

The other part of the output of the frequency ,step-down circuit 342 goes to the frequency stepup circuit 346, where it is converted from frequency jo to (a+1)fo. Frequency step-up circuit 346 may comprise, for example, two tandemtuned stages, which were arranged in accordance with one embodiment constructed by the applicant so that the rst stage selected the 9th harmonic of the square wave input, following which, this 9th harmonic was made to overload a vacuum tube stage, and the 11th harmonic of the resultant signal was selected by another tuned circuit in the output of the latter overload stage. This gave a combined frequency multiplication of 11X9 or 99 times, resulting in a frequency of 10,102.04| cycles per second in the embodiment constructed. ,I

The output of frequency step-up circuit 346 is transmitted through phase shifter 341, which is of the same type as phase shifter 321. The output of phase shifter 341 is applied to the input 4of square wave generatorI 348, which is similar to square wave generators 33| and 350 in principle, producing a square wave output having a frequency (a+1)fo which is impressed on the X- axis sweep voltage generator 339.

It will be seen that X-axls sweep voltage generator 339 has as input signals, three square wave signals having respective frequencies of afo. (a+1)fo, and fo. In the embodiment previously mentioned. these frequencies were 10,000, 10,102.04+, and 102.04+ cycles per second. 'Ihe manner in which X-axis sweep wave generator 339 operates to produce the X-axis sweep voltage from these input signals will be explained in connection with Fig. 6 of the drawings. The input leads 634 are connected to the output terminals of square wave generator 33|, and the afa frequency square wave, which is at a high amplitude, is transmitted through transformer 635 to the grid of vacuum tube 631 .which is'connected in series with a resistance 636. This large square wave signal on the grid of vacuum tube 631 alternately cuts it off, and permits it to conduct plate current During the half cycle when the grid of tube 631 is being driven positive with respect to the cathode, plate current flows from direct-current potential source 639 through resistance 638 to positively charge condenser 60|. During the alternate half cycles when tube 631 issEl cut oil', no current ows to charge condenser The discharging of condenser 60| is accomplished under control of the other two square wave input signals as follows. The square wave output signal of square wave generator 348 is applied to terminals 644 to which are connected small condensers 6|0 and 6|| leading to the grids of the conventional triode vacuum tubes 602 and 603, respectively. The grids of tubes 602 and 603 are connected through resistances 6| 2 and 6|3 to a direct-current source of potential 6|4 which is negative with respect to ground. The time constants of condenser 6|0 with resistance 6|2, and of condenser 6|| with resistance 6|3, are small so that the signals applied to the grids of tubes 602 and 603 resulting from the square Wave input to terminals 644 take the form of a series of short pips, as illustrated in Figs. 'IA and 7B.

The output of square wave generator 350 is connected toterminals 643, which in turn are connected to the cathodes of conventional vacuum tubes 602 and 603. Resistances 605 and 606 are connected from cathodes of tubes 602 .and 603. respectively, to ground. 'I'hus on one half cycle of the square wave input to terminals 643, the cathode of tube 602 may be driven several 13 volts positive with respect to ground while the cathode of tube 603 is driven several volts negative. On the next half cycle, the polarities on the cathodes are reversed. Fig. '1C illustrates the wave form of the voltage applied to these cathodes.

The direct-current biases on the grids of the I tubes 602 and 603, the amplitudes of the square wave signals applied to the cathodes, and the pips applied to the grids, are all so adjusted that plate current only flows in either of the tubes if a positive pip is applied to its grid while its cathode is driven to a negative potential with respect to ground by the square Wave input to terminals 643. The plates of tubes 602 and 603 are respectively connected in parallel to the primary of transformer 608 and receive directcurrent power from potential source 604.

If the inputs to the two grids of tubes 602 and 603 are 'as shown in Figs. '1A and 1B, and the cathodes are driven by a square' wave as shown in Fig. 7C, the sum of the two plate currents will be a series of pips as shown on Fig. 7D. It will be observed that the pips come at regularly spaced intervals equal to l (a+1) fn seconds except at the times when the square wave shown on 1C changes from a positive to a negative value, or vice versa. At that time, the period between output pips is one-half as long as during the remainder of the cycle.

The pips as--shown on Fig. '1D operate through transformer 608 to trigger off a blocking osciln lator comprising theconventional triode tube I6 I 5. The grid of tube 6| 5 is biased negatively with respect to the cathode by direct-current potential source 6 I 6. The pips appearing at the secondary of transformer 608 cause the potential of the grid of tuber 6|5 to rise from below cut-off to a less negative bias at which plate current starts to ow in tube '6I5. This plate current flowing through winding 622 of a three-winding transformer 6I1 induces a voltage in winding 6|3 of that transformer which is connected in series with the grid of tube 6I5. The induced voltage is in the direction to make the grid more positive and is of such magnitude that it makes the grid draw current by making it positive with respect to the cathode. This current flowing through a circuit comprising condenser 620 'and resistance 6|9. charges condenser 620 in a direction such as to tend to make the grid negative. Thus oscillations are not continued, but after one half cycle. the grid 'assumes a very large negative potential until some of the charge on condenser 620 leaks off through resistance 6I9.

This complete cycle of operation of the blocking oscillator results in a very short pulse of current in the plate circuit of tube 6I5 for every pip of the signal as shown on Fig. 1D. This short surge of plate current also induces a short pulse of voltage in winding 623 of transformer 6I1,

which in turn applies a short pulse of voltage to y the grid of tube 624 to drive it from its normal quiescent bias at cut-off, up to a positive potential With respect to the cathode.. The cathode of tube -624 is,I biased negatively with respect to ground by potential source 626. and the grid has a cut-off bias with respect to cathode supplied by potential source 621. The plate of tube 626 is connected to condenser 60| whereby flow olf plate current in tube 624 discharges condenser 60|.

As previously mentioned, this plate current flow is controlled by very short voltage pulses applied to the grid so that condenser is discharged very quickly.

The wave form of the input to terminals 636 is shown in Fig. 7E. If it is assumed that tube 631 is cut off when the voltage as shown in Fig. 7E is negative, and that charging current flows to condenser I, through tube 631. when the voltage as shown in Fig. '7E is positive, and that condenser 60| is discharged quickly at each pip of the wave form shown in Fig. 7D, the resultant wave shape across condenser 60| will be as shown in Fig. 7F. The horizontal stair steps in the Wave form of Fig. 7F correspond to the intervals when tube 631 is cut off. The diagonal parts correspond to the charging of condenser 60|, and the vertical parts correspond to the practically instantaneous discharging of condenser 60| through the plate circuit of tube 624.

The illustrations of Figs. 1A to '1F show Wave shapes corresponding to the condition when a is l0, which is a comparatively low value. In this case, there are only five stair steps inthe fundamental period of the wave shape of Fig. 7F. In the embodiment of the previously-mentioned circuit which was constructed, the value of a was 98 and the wave shape corresponding to Fig. 7F had. 49 stair steps per fundamental period. In general, a would preferably be a larger number than 10.

The preceding description has .outlined one -method of obtaining the desired wave shape for the X-axis sweep voltage. There are other methods, one of which utilizes the circuit illustrated in Fig. 8. When this circuit is used as the X-axis sweep voltage generator 339 of Fig. 3A, two modifications of the circuit of Fig. 3A are required. The frequency step-up unit 346 must multiply the frequency fo by a factor 2(a+l) instead of by the factor (a-l-l) and the fn square wave input to the X-aXis sweep voltage generator 339 from square wave generator 350 is not needed. so that square Wave generator 350 may be omitted.

Referring again to Fig. 8, input terminals `8311 are connected to the output of square Wave generator 33| of Fig. 3A, and input terminals 844 are connected to the output of square wave generator 348 of Fig. 3A. Transformer 835, resistances 836 and 830, tube 831,-condenser 80| and potential source B39 perform identical functions to those of transformer 635, resistances 636 land 638, tube 631, condenser 60| `and potential source 639, respectively of Fig. 6. By means of these circuit elements, condenser 80| is allowed to charge pe-- riodically under control of the input at terminals 834, the wave shape of which is illustrated on Fig. 9B.

The discharging of condenser 60| is performed by tube 824 under control of blocking oscillator tube 8|5 in the same manner as condenser 60| of Fig. 6 was discharged by tube 621i under control of blocking oscillator tube 6I5. The associated circuit elements namely, transformer 8I1, potential sources 8I6, 826 vand 821, resistances 8I9 and 828, and condenser 820 perform functions identical to those explained in connection with transformer 6I1, potential sources 6|6, 626 and 621, resistances .6I9 and 628, and condenser 620 of Fig..6.

The input signal to the gridof the blocking oscillator differs from the caseY described with reference to Fig. 6 and is shown in Fig. 9C. This input signal is the sum of the voltages supplied through transformer 808, and the voltage appearing 'across resistance 8|2. Condenser 8I| is a l5 small condenser, and resistance SI2 is relatively small, so that with a square wave applied to input terminals 844, short pips will be obtained across resistance 8I2 because of the differentiating action oi' condenser BII and resistance 8I2. The voltage appearing a'cross resistor 8I2 is shown in Fig. 9A. 'I'his wave shape, when combined with a voltage having the wave shape of Fig. 9B, gives the resultant voltage of Fig. 9C to be applied to the grid of tube 8I5. 'I'he normal negative bias on the grid of tube 8| S'Which is supplied by direct-current potential source 8I6, prevents any flow of plate current in tube 8I5 except during the very short intervals of the signal shown on Fig. 9C when the positive pips are superimposed on the positive halves of the square wave signal. When this flow of plate current is initiated in tube 8I5, the very short -voltage pulse is applied.

to the grid of tube 324 to make its plate circuit discharge condenser 80| in the same manner as described in connection with Fig. 6.

The timing of these discharge pulses is seen to be the same as that obtained with the circuit of Fig. 6, and in combination with the charging function controlled by square wave input to the tube 831, resu/l'ts in a wave shape across condenser 80I such as is shown in Fig. 9D. This is the desired wave shape for the X-axis sweep voltage.

It has been shown how the sweep voltage generator 339 of Fig. 3A may be constructed in two different ways. The output wave shape in either case is the same, and is applied to the input of amplier 34|. The output of amplifier 34I is connected to the horizontal deflection plates 3II of the storage tube 30| The voltages applied to deflection plates 309 and 3l I, having wave shapes like those of Figs. C and 5B, respectively, cause the electron beam to move in a path as indicated in Fig. 5A.

The manner in which the motion of the beam on the target mosaic 3 I 0 is synchronized with the signal recording and wiping operationswill be understood from the following discussion.

Referring again to Fig. 3A, signal input to thesystem is applied through leads 356 to a gating circuit, comprising series resistance 351 and crystal diodes 358, on which is impressed a square wave signal having a frequency ajo applied-through transformer 351i. Diodes 358 are vrectifying devices, such as the well-knowngerl vof tube 360 is obtained across resistance 332, and impressed on the storage tube mosaic grid BIZ.

As described in the preceding paragraph, the

operation oi' the input gate using crystal diodes manium or silicon crystal rectilers widelyused in microwave detectors. During the first half of the square wave voltagecycle when the 'voltage applied through transformer 354 to diodes 358 is in the direction of easy current iiow, the alternating-current impedance of the diodes 358 is low so that the signal tending to appear on the grid of vacuum tube 360 is shunted to ground through the aforesaid low impedance of the crystal diodes 358 and the secondary oftransformer 354. On the other half cycle of the square wave applied voltage, the crystal diodes 358 have a high impedance, and the incoming signal is not appreciably shunted to' ground. The frequency of the square wave voltage is at least twice as great as the highest input signal frequency, so that the signal which is applied to the grid of vacuum tube 360 consists of alternate sections'of the input signal wave forni, interspersed with sections of zero signal voltage. Vacuum tube 360 is supplied with plate potentialfrom potential source 3I6, and a resistor 362 is connected between its cathode and ground, making it a cathode follower stage. A replica of the signal applied to the grid 358, is synchronized with the sweep of the beam by the afo square wave impulse so that the input signal to leads 353 is shunted to ground during the intervals when the beam is proceeding along a diagonal path over the target mosaic 3I0, and the input signal is not shunted but appears on the mosaic grid 3I2 during that part of the cycle when the beam is'moved along a vertical path. During the interval when the beam is moved along the vertical path, the mica surface adjacent to the mosaic grid 3I2 on which the beam impinges, is charged at each point to a potential corresponding to the instantaneous value oi the input signal voltage on the mosaic grid 3I2 at that time.

The charging and discharging of the target takes place through a mechanism involving a -transfer oi secondary electrons between the mica element 3I3 and the grid 3I2. During those periods when the potential of the grid ispositive with respect to the spot on the mica lmpinged by the beam, secondary electrons, in excess of unity ratio, will move from the mica to the grid, leaving a positive charge on the spot with respect to adjacent spots. If, however, the grid isI negative with respect to the mica spot impinged by the beam, the secondary electrons will be repelled from the grid, causing the mica spot to become more negative. Thus, it is apparent that during the recording operation, while grid 3I2 is potential varied under control oi impressed signal voltages, the mica element 3I3 will store a charge record which varies from point to point asthe intensity of the signal.

During the succeeding wiping period in which the beam moves over the target diagonally, the mosaic grid 3I2 is held at constant or reference potential, andI the mica surface of target 3| 0 traversed by the beam spot is discharged point by point to this reference potential, whereby the recorded charge is neutralized leaving the mica element 3I3 at a constant potential for a repetition of the recording operation. During this discharging of the front surface of the mica, capacitive currents are caused to iiow in the bars on the back surface of the mica plate. Thus, if the potential of a small area on the front surface of the mica is caused to change by a few volts, a bar directly behind this` small area will have its potential correspondingly changed in an amount depending on the capacity between the small area on the front and the bar on the rear of the mica.

The bars' al4a, smb, amc and sullaare eo'nnected to the gridsgf tubes 3I8a`, 3I8b, 3l8c 'and 3I8d, respectively, 3l 8d are shown on of -which only tubes 3I8a"and Fig. 3A. In addition, each b ar is. also connected to a clamping circuit which is arrangedto shunt the bar to ground through nected to a source of square wave signals,

namely, the secondary of transformer 3i'l. The center tap of the secondary of transformer 3l7 is connected to ground. The operation of this clamping circuit is thus similar to that of the input gate circuit including crystal diodes 358 -1-7 L18v and transformer 3N, described previously. 'The 'tcntial'variations on the grid will be transmita other crystal diodes 3I3b. 315e and 3|5d are aro without phaseshift. However, if resistance 31 ranged in a similar manner to clamp b ars 43141i. is connected to the plate a phase reversal resul Ille and 3I4d. yAll of these crystal diodes re- Both ways of connecting the weighting resistan ceive their driving voltage through the one trans- 5 322 are desirable il' the "gv-func,tior icontaii Y former 311, so that' -all bars are simultaneously both positive' and negative values. In the ca: either shunted to ground, or l'effectively unoi' Fig. 3A, resistancezaa is shown connectedl shunted depending on the polarity of the square the plate of tube 3I3a; and resistance 322d wave drive voltage. shown connected to the cathode of tube 3l8d.y l The source of square wavevoltage for the vbar 1o general, the valuesof resistances-322:1, 322b, 321 clamp circuits comprising transformer 311 and' and`322d will notbelalike, buty .will vary in at crystal diodes 3I5a to 3|3d, inclusive, is square cordancewith the' shape of the g-.function in wave generator 310, similar in principle to the manner to be described later. square wave generators 33|, 348 and 350, whose Allv of the weighting resistanceszz are col output connects to transformer 3H by Way of llinected in parallel. to one terminal of the' rel: leads 313, and whose .input is a sine wave of 'afo tivelysmall resistance 323, the other end of whit frequency derived from the output of phase is connected to'ground. Thus, the voltage mea; shifter 321 by way of leads 328 to amplifier 365. ured Vacross resistance 323 is proportional to tl The output of amplier 365 is split into three sum of all lthe currents rlewingin the weightii parts. One part passes through thenetwork" 2o resistances 322ato 3224i, inclusive. comprising condenser 31| and resistance 312 to It is thus seen Vthat the wave shape of the vol the input of a square wave generator 310. VVThe age appearing across resistance 323 consists function of the circuit comprising oondenSer 37| periods of constantvoltage corresponding to tl and resistance 312 is'to shift the phase of "the interval during which the bars are all shunt@ afo sine wave a small amount so as to make the 25 to ground alternated with periods iny which tl .bar-clamp circuits operate from the shunting to signals are being collected from the bars an the open condition a very short interval after the added in turn as the electron beam sweepsovi moSaio grid iS Switched from the Signal value to the target mosaic 310. During the intervals i the constant value of voltage. thereby avoiding which the signals are. being ooiiected. the voli a large 'transient Surgeoi potential at the bars 30 age across resistance 323 is changing as succe: ldue to the Sudden Shift of Potential on the mosaic sive bar signals are added, the final value of voli grid SI2, which has an appreciable capacity to age across resistance 323 after all the bars hal the bars. been crossed by the diagonal path of the bean A Second Dari? of the Output of amplifier 355 and just before the bars are clamped or shunts iS impressed on a network oompliSing condenser 35 to ground. corresponding to the desired sign: 316 and resistance 311. Vand thence to the input output. Itis at this instant that itis desirab: of Square Wave generator 315. Whose output to gate the voltage through the first output gai drives the first output gate circuit in a manner to condenser 383, homing the voltage on oor tu be described hereinaften The Condenser 375 denser 383 constant at this value, until the ne:

and resistance 311 are adjusted to give a small 40 succeeding cycle of signal collection from tl* phase shift so that the operation of the rst outbars,

Put gate Will be delayed in time slightly with re- The gating of the signal voltage from resistanc Speot to the operation of the bar Clamp Circuit 323 to the succeeding circuit components is pei which is driven by square wave generator- 310. formed by crystal diodes 38u which are driven b The third part of the output of amplifier 365 if, a square wave signal at the frequency of@ or is impressed on a network comprising condenser tained through transformer 319 from the outpt '388 and resistance 389. and thence passes to the of square wave generator 315. Resistance 323 input of Square wave generator 381. whose outconnected to the center tap of the secondary c Put drives the Second output gate in a manner to transformer 319. When the polarity of the squai be described hereinafter; The condenser 388 l-o wave voltage is such as to cause current to o' and resistance 389 provide a Small phase shift to in the forward direction through crystal diode delay the operation of the second output sate rel- 380, their impedance is thereby made relative] ative to operation ofthe first output gatelow. Condenser 333 is connected to a point be In preceding paragraphs of the specification tween crystal diodes 38u, and is charged or die 1t hasbeen shown how the signals are stored 55 charged as the case may be, to the potential c on the mica. and how they result in voltage lead 324 from resistance srs, through the sec Changes on the bars when the bars are unondary of transformer 315i and the low impedanc clamped and the electron beam proceeds along of the diodes. f

a. diagonal path over the mosaic. These small The phasing of the squareV wave .output t voltage changes on the bars control the grid bias o square wave generator 315 -is arranged so the of the conventional three-electrode tubes 3|8a the driving voltage on crystal diodes 380 reverse i5o 3|8d, inclusive. Wheleby Corresponding voltphase at the time when all of the bar signal ages are impressed on the weighting and sumhave been collected.. and just before' the ba ming network following tubes :iisd ilo 3 8d in clamp circuit shuntsA the bars -3Ida to 3141i vt the circuit. The plate circuits of the aforesaid ground potential, With this reversal of polarit: tubes 3l8a to 3I8d are energized by the potenthe crystal diodes 38o are no longer low im tial source 3l9 .through the respective resistances pedances, but liecome very high impedances s 338er to- 398d, and resistances 32Ua to 320d are that in effect, condenser 383 is disconnected fro! cOlmedied between eaiihodeS and ground inicathresistance 323, and any changes in potentie ode follower arrangement- *Weighting resistances 70 across resistance 3.23 then do not influence' th 322ato 322d, inclusive, may beconnected either to .charge on condenser 383.` Thus it will be see the plates or vcathocles of tubes 3I8a to 3|8'd with that during the major part of the interval whil one resistance connected to each tube. If, for exsignals are .being collected from the bars 3Ma t ample, -a weighting resistance 322 is connected to 3I4d. inclusive, condenser 383 is connected to re a cathode of a tube 318, alternating-current po- '(5 sistance 323 through the first output gate. an

sa,osi,eoo

that during this interval, the potential on condenser 333 is changing as successive baisignals 383 is applied to the grid li tube 38h-the Plate of which is energized by potential source 382. A resistance 385 is connected between the cathode oi' tube 33| and ground. and the output signal is taken across this resistance, thusconstituting a cathode follower arrangement of tube 38|. The signal voltage appearing across resistance 385 is essentially the same in wave form as that appearing across condenser 333. .I n order to remove the variations in this wave form corresponding to the collection of signals from bars 3|Ia to 3i4d. inclusive, a second output gate is arranged to close a conducting path between resistance 385 and condenser 399 during the interval when the iirst output gate is open. 'I'he charge on condenser 383 is thus quiescent at a value corresponding to the desired signal value.

The second output gate referred to above uses crystal diodes 392 and transformer 390, a. square wave driving voltage being obtained from square wave generator 381, whichalternately makes the impedance of diodes 392 low and then high, de-

-pending on polarity of driving voltage. Resist ance 385 is connected to the center tap of transformer 390. and condenser 399 is connected to the point between crystal diodes 392. With the exception of the shift in timing of the two square wave driving voltages, operation of the second output gate is substantially the same as that of the iirst output gate,` the second output gate being timed to make crystal diodes 392 low impedance during the interval when crystal diodes 380 are high impedance, and vice versa.

The-signal appearing on condenser 399 is applied to the grid of tube 393, the plate circuit of which is energized by potential source 396. Thus, the final output signal is taken across resistance 396 which is connected between the cathode of tube 393 and ground.

In order to more clearly indicate the manner in which the system of Fig. 3A of the drawings functions in accordance with the theory discussed in the early part of the specification, to modify an impressed' signal in accordance with a pre,

selected characteristic, simplified diagrams of the recording and wiping operations of the electron beam 302 on the target 3H) are shown in Figs.

11A, 11B, and 11C. 'Ihese will now be described.'

Assume that the network response to be simulated by the system of Fig. 3A has a g-function or impulse response characteristic vof the form indicated in Fig. of the drawings.

by go, y1, y2 and gs, hates of the g-function curve selected at equal intervals Ar from time t=tn to time t=nAr, which represents substantially the complete pe- This may' be approximated by a series of values represented which are seen to be. ordiindividual amplifier tubes sistance elements 32m-3nd to a. common output circuit. For simplicity oi' illustration, the ampliner tubes, bar clamps, and output gate circuits, have been omitted from Figs. 11A, 11B and 11C and the weighting resistance elements and the respective re- 322a-322ii shown as connected directly to the respective target elements lilafllld. Each oi' the weighting resistors is given a value which corresponds to an ordinate of the a-function indicated in Fig. 10, so that element 322a is assigned a value proportional to the ordinate m=g(3A1-), element 3221 a value proportion to -gz=g(2Ar), etc. The beam moves over the target'3i0 to perform the recording and wiping operations in a manner shown and described with reference to Fig. 5 hereinbefore. Referring to Fig. 11A, let us assume, for'the present, that the scanning beam performs only the recording operation by moving up the target in a series of parallel vertical lines, which for the purposes oi' simplifying the explanation, have been reduced to four. The periodfor completion oi the scanning operation from left to right across the target is determined by the period of duration of the g-function, which in this case is equal to BA1. The order in which the beam in wiping position neutralizes the charges deposited on the target 3io will now be described with reference to Fig. 11C, which shows a simpliiied diagram oi' the operation. It will be assumed that the beam has just completed one scan of the target from get, during which interval the columns oi' charge riod of duration of the g-function. In order to simplify the present illustration, the selected g-function will be represented by only four ordinates, although it is apparent from the discussion in the early part of the specication that many more ordinates may be required to give a workable approximation of the chosen function. Henc the target sill, as described with reference backing elements, which are connected through Fig. 3A, is equipped with four transverse recorded will be proportioned as indicated in Fig.

Prior to the recording of the vertical column I, the beam traces an' oblique wiping line AA'. illes back from right to left across the line A'B. and traces the' oblique line BB', which positions the beam to commence the recording of vertical column I. It is apparent that the charges neutralized by the beam as it traces the wiping scanning line AA', are charges which were recorded on the target during the previous interval of scan, and which have values such as indicated in Fig. 11A. The positionof the wiping line AA', which is directed diagonally from the upper left-hand corner to the lowerV righthand corner of the target 3io, is determined by the points of intersection of each of the target elements iliwfd) taken in succession from top to bottom with one of the recording scanning lines I-IV, taken in succession from left to right. Thus as the beam traces the line AA', neutralizing recorded charges on the mica face 3| 3 of the target 3m, the following proportionate charges are released from the transverse backing elements 3M:

For the purposes of this discussion, the horizontal fly-back of the beam from A to B will be neglected. Because of its position. no charge is released during the oblique scan BB'.

After the beam has executed the vertical scanning line I, whereon the recorded charge assumes the values indicated in column I of Fig. 11B, the beam traces an oblique wiping line CC',

2l which is parallel to the wiping line AA', and determined by the points of intersection between the top three target element 3I4a, 3Hb and 3I4c and their respective points of intersection with the recording line II, III and IV, taken in succession.

Referring still to Fig. 11A, assume that the beam reaches the right-hand recording position on the target designated as column IV at a reference time t=tn, then column I on the lefthand side of the target must have been recorded at time t=(to-3Ar), column II at t=(tu-2Ar), and column III at t=(t-Ar). Assuming that the time required to scan from the bottom to the top of the target is negligible, columns of charge are laid down which are proportional to the following values:

4 Assume now, that the charge has been cornpletely wiped from the target, and that the scanning beam is again returned to the left-hand side of the target to repeat the recording operation. The new columns of charge laid down on the target will be proportional to the following values, as shown in Fig. 11B of the drawings.

The foregoing description with reference to Figs. 11A and 11B has been concerned only with the recording operation of the beam. As described hereinbefore with reference to Fig. 4, after each successive vertical scanning line, the beam is deflected to scan the target in a corresponding pair of obliquely directed lines for the purpose of releasing the increments of charge on the transverse backing elements to ow into a common output in a. predetermined order. As the beam in wiping position neutralizes an increment of charge on a given one of the elements 3M, current proportional thereto flows through the corresponding one of the weighting resistance elements 322, and is further proportioned in accordance with a. given ordinate of the selected g-function. The following charges are released from the transverse backing elements by this operation:

After the beam has executed a. return scan from point C to point D, another wiping line DD' is traced. It is apparent that the charges released during the wiping operation DD' are the newly recorded charges that have been laid down by the beam during the present interval of scan, and which assume the values indicated in Fig. 11B. Therefore, the charge released by the scan DD' is from a single transverse target element, and assumes the following value:

In a similar fashion, after the recording of columnvII, the wiping beam traces the oblique line EE', releasing increments of charge;

and the line FF', releasing increments of charge:

suc; EnH-Afri. and; maw/MAT After the recording of column III. the wiping beam traces the line GG', releasing increments of charge:

and the line HH', releasing increments of charge:

I put circuit:

Referring to Equation 2 derived in the early part of the specification, it is seen that th-e summation of the charges released during the scan of the beam along line AA is an approximation of the response integral for time t=to, and may be generalized by the following equation:

where Qito) represents the total charge collected at time t=to, and r varies by integral values of n from 0 to (nm), where no1- is the period required to completely represent the chosen g-function.

Assuming for the purposes of approximation, that the wiping operations along lines CC' and DD' occur at the same time, a period later by the interval A-r than the wiping operation along the line AA', it will readily be seen that the summation of the charges released during these two scanning periods gives an approximation of the response integral for time t: (to-l-Ar) which may be generalized as follows In a. similar manner, it can be shown the sum of the charges released along the scanning 'lines EE and FF approximates the response integral for time t=(t0+2i1), and the sum of the charges released along the scanning lines GG and HH approximates the response integral for time t=(to+3A-r). Thus, it can be seen from the foregoing simplied explanation, that the output of the system of Fig. 3A progressively approximates the response integral at each of a succession of equally spaced points in time, the prox- 23 imity of which depends on the physical limitaP tions of the apparatus.

It will be understood that the system of the present invention is not limited to the use of any element or combination of elements disclosed by way of illustration in this speciilcation and the attached drawings; and that the principles of the present invention are capable of embodiment in other forms than those specifically disclosed.

What is claimed is:

1. The method which comprises progressively producing a series of linear coextensive parallel records in space which vary from one to another in accordance with the instantaneous values of v a given signal after each of a succession of equal time intervals, during each said interval neutralizing points on a given number oi adjacent records of said series in rotation to produce a succession of samples proportional to each of said records, said points disposed along a line obliquely directed withrrespect to said records, weighting each of said samples in`rotaticn in accordance with selected values of a chosen weighting function, integrating the weighted samples in a common output circuit, and repeating said neutralizing. weighting, and integrating steps duringA each succeeding interval commencing with the record next adjacent to the record with which the previous operation commenced.

2. The method which comprises under control of an electron beam progressively producing a series of linear cdextensive parallel charge records on a target interposed in the path of said beam which vary from one to another in accordance with the instantaneous values of a given signal after each of a succession of equal time intervals, during each said interval under control of said beam neutralizing points on a given number of adjacent records of said series in rotation to produce a succession of currents from said target which are proportional to each of said records, said neutralized points disposed along a line obliquely directed with respect to said records,

weighting each of said currents in accordance with a. selected value of a chosen weighting function, integrating the Weighted currents in a common output circuit, and repeating said neutralizing, weighting, and integrating steps during each succeeding interval commencing with the record next adjacent to the record with which the previous operation commenced.

3. The method in accordance with claim 2 in which the step of producing under control of an electron beam a series of linear coextensive charge records on said target comprises controlling secondary radiation from said target at the successive points impinged by' said beam by varying the electrical ileld adjacent said target in accordance with variations in the intensity of the applied signal.

4. The method in accordance with claim 3A in which the step of, under control of an electron beam, neutralizing points on a given number of adjacent records of said series in rotation to produce a succession of currents from said target which are proportional to said records comprises controlling secondary `radiation from said target at successive points impinged by said beam by maintaining the electrical field adjacent said target at a constant reference potential.

5. A system for simulating network response which comprises in combination a, signal source, a source of a beam of electrons, a target interposed in the path of said beam, deflecting means comprising a circuit for causing said beam to periodically assume diilerent scanning directions in alternate succession for concurrently scanning said target in two series of substantially parallel lines, said series having obliquely related directions in the plane of said target, recording means under control of said beam in one of said scanning directions to produce a record oi' charge on said target which varies from one to another of said lines in accordance with the amplitudetime variation in said signal, charge-storing means included on said target for storing increments of said record of charge on successive portions of said target, neutralizing means under control of said beam in another of said scanning directions to release increments of charge from certain portions of said target representing diiferent instantaneous signal values during a selected past interval of said signal, means including a plurality of circuits individually connected to said charge-storing means for weighting each` ing means through said weighting circuits to produce a modified output signal, and means comprising a synchronizing circuit connected to said recording means, said neutralizing means, and said output circuit to initiate periodic repetition of a cycle including said recording, neutralizing, weighting, collecting and integrating operations.

6. A transducer comprising in combination a signal source, a source of a beam of electrons, a target interposed in the path of said beam, and a deilecting circuit for causing said beam to assume in periodic succession a iirst, a second, and a third scanning direction for scanning said target in three series of scanning lines individually laid down in alternate succession, the lrst said series comprising a progression of substantially straight parallel lines positioned at spaced intervals across the surface of said target, the second said series comprising a progression of substantially straight parallel lines obliquely directed with respect to the lines of said first group in the plane of said target. each line of said second group progressively positioned to immediately precede a. corresponding line of said iirst group, and the third said series comprising a progression of substantially straight parallel lines obliquely directed in the plane of said target with respect to the lines of said first group and parallel to the lines of said second group, each line of said third group progressively positioned to immediately succeed a corresponding line of said rst group, means under control of said beam in said rst scanning direction to produce a record of charge on said target which varies in accordance with the time variations of said signal, chargestoring means for storing increments of said record of charge on successive portions of said target, neutralizing means under control of said beam in said second and third scanning positions to release increments of charge from a series of positions on said target representing different instantaneous signal values during a selected past interval of said signal, means including a plurality of circuits individually connected to said charge-storing means for Weighting the incre? 25 said weighting circuits to produce a modified output, and means comprising a synchronizing circuit connected to said recording means, said neutralizing means, and said output circuit to initiate periodic repetition of a cycle including said recording. neutralizing, weighting, collecting and integrating operations.

7. A frequency selective system comprising in combination an electrical signal sour, a cathode-ray tube having means for producing a beam of electrons. a composite target interposed in the path of said beam, said target comprising a plurality of elements including charge-storing means, said tube having deiiecting means for moving said beam to repeatedly scari the elements of said target, means under control of said beam to produce a record of charge which varies from point to point on said target in accordance with the instantaneous values of amplitude of said signal. said charge-storing means varying from one to another of saidtarget elements for modifying the increments o f output current from successive target elements in accordance with selected values of a weighting function, an output circuit, and means under control of said beam to discharge into said output' circuitthe weighted increments of charge from said target elements in a preselected order whereby to produce a modied output current.

8. A system for simulating network response which comprises in combination a cathode-ray tube having a source of a beam of electrons, a target interposed lin the path of said beam, defleeting means for directing said beam to trace the components of a first series of parallel lines across said target in alternation with the components of a second series of parallel lines, the two said series of lines being obliquely related in the plane of said target, a grid adjacent to the surface of said target in the path of said beam, means recurrently operative in synchronism with said beam while said beam traces a component of one of said series to impress on said grid potential variati-ons in accordance with the amplitude time variations of an impressed signal, whereby secondary radiation from said target under control of said beam produces a record of electrical charge thereon, means recurrently operative in synchronism with said beam while said beam traces a component of a second of said series to impress on said grid a constant reference potential whereby under control of said scanning beam increments of charge proportional to said record are simultaneously released from certain portions of said target, said increments representing different instantaneous values in the history of said signal, means for weighting each of said increments of charge in accordance with selected values of a predetermined function, and means comprising an output circuit connected to collect and integrate said increments Aof charge received from said target and said weighting means to produce a modined output.

9. A frequency selective system comprising in combination an electrical signal source, a cathode-ray tube having means for producing a beam of electrons, a target interposed in the path of said beam, said target comprising a plurality of charge-storing elements, said tube having deflecting means for moving said beam to repeatedly scan said target, means comprising a grid ad- `jacent the inner surface of said target having its potential varied in accordance with the signal from said source, said grid operatingunder control 'of said beam to produce a record of charge 'a preselected order whereby to produce a modifie:

output current.

l0. A system for modifying an impressed electrical signal in accordance with a. desired characteristic which comprises in combination ai electrical signal source, a cathode-ray tube including a source offa beam of electrons, a targe disposed in the path of said beam comprising i plurality of separate charge-storing elements disposed in transverse parallel array, beam deflecting means comprising a sweep circuit for con trolling said beam to repeatedly scan said tar get in a configuration comprising a first and a second series of obliquely disposed parallel line; each cutting a plurality of said target elements said lines individually laid down in alternan succession, an electrical circuit including thu source of said beam connected to said signa source for depositing a charge on said targe elements which varies from line to line in saii first series in accordance withthe instantaneou variations in the amplitude of said signal, mean; operative under control of said beam to releas the charge deposited on said target elements fron line to line in said second series, a plurality o weighting circuits each presenting a difieren preselected value of attenuation respectively con nected to said charge-storing target elements and an output circuit connected to said weightim circuits to receive the charge from said charge storing target elements.

11. A `system for modifying an impressed elec trical signal in accordance with a desired char acteristlc which comprises in combination ai electrical signal source, a source of electrical syn chronizing signals, a cathode-ray tube includin a source of a beam of electrons, a target dispose -in the path of said beam comprising a pluralit of electrically insulated charge-storing element disposed in transverse parallel array, a grid dis posed adjacent to the surface of said target i the direction of said beam, a direct-current po tential source, a rst gating circuit controlled b said synchronizing source and alternately oper ative during a first period to connect said gri to receive energy from said signal source, an during a second period to connect said grid t said direct-current source, beam deflecting mean comprising a sweep circuit connected to sai synchronizing source for controlling said bear to repeatedly scan said target depositing charg in a configuration comprising two series c obliquely disposed parallel lines each cutting plurality of said target elements, said lines in dividually laid down in alternate successio: during said iirst period and said second perioc a, plurality of weighing circuits each present ing a different preselected value of attenuatioi respectively connected to said charge-storm target elements, an output circuit, and mean comprising a second gating circuit controlled b said synchronizing source which operates alter nately during said first and second periods t control the connection of said output circuit t receive energy from said charge-storing targe elements through said weighting circuits. 

